The present application claims priority from European patent Application No. 01830701.7, filed Nov. 14, 2001, which is incorporated by reference.
The present invention refers generally to methods for the manufacture of electromagnetic radiation reflecting devices. In particular, one embodiment of the invention refers to the fabrication of reflecting devices comprising silicon substrates provided with a wall having the function of a mirror and usable, for example, in the photonic field.
As is known, reflecting devices, hereinafter called mirrors, are used to deflect a beam of incident radiation, or light, at an appropriate angle.
For example, in the field of telecommunications, mirrors are used as an interface between optical fibers and transmitting/receiving devices. According to a known fabrication method, the optical fiber is inserted into a silicon substrate and one end of the fiber, suitably cut and polished, is covered with a layer of reflecting aluminum inclined at 45xc2x0 in relation to the fiber axis.
This mirror placed at the end of the fiber deflects the light beam by 90xc2x0 which, after passing through a suitable glass covering element, reaches, for example, a photo-detector. Several optical fibers can be inserted into the substrate in U-grooves obtained by means of mechanical micro-machining of the substrate itself. Typically, the grooves have one side of 125 xcexcm and a pitch of 250 xcexcm.
In another application, the mirrors are used to deflect (typically by 90xc2x0) the light emitted by a laser source to hit an Optical Compact Disc (OCD) in a reading process.
A conventional method for manufacturing mirrors used for OCDs comprises the steps of micro-machining glass bars in order to form a mirror wall, followed by a welding operation of said bars on to silicon wafers used for the correct alignment of the devices.
The methods based on micro-machining of substrates or silicon bars are both complex and costly, so research into alternative methods is attractive.
In the article xe2x80x9cFabrication of 45xc2x0 Optical Mirrors on  less than 100 greater than  Silicon Using Surfactant-added TMAH Solutionxe2x80x9d M. Semikura and H. Naruse, Transducer ""99; Jun. 7-10, 1999, Sendai Japan, a mirror fabrication method is described in which the silicon support is etched chemically by an anisotropic agent. According to this method, the silicon support has an orientation of  less than 100 greater than  and is etched, through a suitable oxide mask formed on its external surface, with a solution (at a temperature of 90xc2x0 C.) containing the anisotropic agent Tetramethylammonium Hydroxide (TMAH) to which a surfactant has been added. The TMAH agent cuts into the silicon substrate  less than 100 greater than  giving rise to free parallel walls with crystalline planes {110}. According to the authors, this chemical etching makes it possible to obtain a wall parallel to the planes {110 and, therefore, inclined at 45xc2x0 in relation to the external surface of the substrate  less than 100 greater than .
The authors of the article report that they obtained, with the above-mentioned method, walls at 45xc2x0 having a root-mean-square of roughness equal to 50 nm and peak-to-valley values of around 200 nm.
It should be noted that these roughness values make the method proposed in the article unsuitable for the production of mirrors destined for photonic applications, such as those mentioned as an example above. In fact, this type of application necessitates a reflection quality higher than that obtainable with mirror walls having the roughness indicated in the article.
An embodiment of the present invention is to propose a method for manufacturing reflecting devices which overcomes the limits and disadvantages of the methods described above with reference to the known art.
Other embodiments of the invention include a device for the reflection of electromagnetic radiation and a system using a device for the reflection of electromagnetic radiation.